Germanide Formation Research Articles

Conversion of 2D MXene to Multi-Low-Dimensional GerMXene Superlattice Heterostructure.

Integration of 2D structures into other low‐dimensional materials results in the development of distinct van der Waals heterostructures (vdWHSs) with enhanced properties. However, obtaining 2D–1D–0D vdWHSs of technologically useful next generation materials, transition‐metal carbide MXene and monoelemental Xene nanosheets in a single superlattice heterostructure is still challenging. Here, the fabrication of a new multidimensional superlattice heterostructure “GerMXene” from exfoliated M3X2T x MXene and hydrogenated germanane (GeH) crystals, is reported. Direct experimental evidence for conversion of hydrothermally activated titanium carbide MXene (A‐MXene) to GerMXene heterostructure through the rapid and spontaneous formation of titanium germanide (TiGe2 and Ti6Ge5) bonds, is provided. The obtained GerMXene heterostructure possesses enhanced surface properties, aqueous dispersibility, and Dirac signature of embedded GeH nanosheets as well as quantum dots. GerMXene exhibits functional bioactivity, electrical conductivity, and negative surface charge, paving ways for its applications in biomedical field, electronics, and energy storage.

Swelling and sputtering of porous germanium by silver ions

Abstract Surface processes for porous Ge (PGe) formed by low-energy high-dose implantation of Ag+ with an energy of E = 30 keV and a current density J = 5 μA/cm2 in dependence of the radiation dose D = 6.2·1014–1.5·1017 ion/cm2 where observed. Using X-ray photoelectron spectroscopy, it was found that for selected implantation conditions at D ≥ 9.3·1015 ion/cm2, Ag nanoparticles were synthesized in Ge, but formation of silver germanide (GeAg4) was not occur. Using scanning electron and atomic-force microscopy it was found that with increasing D up to ~1.9 × 1016 ion/cm2 , a layer of porous germanium (Ag:PGe) is formed, accompanied by swelling of the implanted Ge surface up to 25 nm thick. With a further increase of D > 1.9·1016 ion/cm2, the opposite effect is observed, which consists of sputtering PGe at a constant rate of ~3.6 nm/min and an sputtering yield of ~17.2.

Enabling Low Contact Resistivity on n-Ge by Implantation After Ti Germanide

The process to form Ti germanide on P-implanted Ge ( $ {2} \times {10}^{ {19}}$ cm−3) with low contact resistivity ( $\rho _{c}$ ) was developed. Sequential deposition of Ti and TiN on n-Ge without annealing leads to rectifying ${I}$ – ${V}$ characteristic due to Fermi level pinning. With 600 °C annealing, Ohmic-like ${I}$ – ${V}$ behavior was achieved due to Ti germanide (C54 phase included) formation that depins Fermi level and makes $\rho _{c}$ of ${1.5}\times {10}^{{{-{5}}}} ~\Omega -\text {cm}^{{{2}}}$ and Schottky barrier height for electron ( $\Phi _{\text {BN}}$ ) of 0.22 eV. Even for 700 °C annealing, the Ti germanide exhibits comparable $\rho _{c}$ and good thermal stability without agglomeration, which is a concern of NiGe. By adopting additional P implantation after germanide, $\rho _{c}$ and $\Phi _{\text {BN}}$ can be further improved to ${3.6}\times {10}^{{{- {6}}}}~\Omega $ -cm2 and 0.17 eV, respectively. The improvement is ascribed to the enhanced dopant segregation at the germanide/Ge interface that results in stronger dipoles and more significantly reduced $\Phi _{\text {BN}}$ and $\rho _{c}$ . The Ti germanide process paves a promising path to enable a next-generation Ge technology.

A study on NiGe-contacted Ge n+/p Ge shallow junction prepared by dopant segregation technique

In this work, the effect of dopant segregation on the NiGe/n-Ge contact is studied by experiments and first-principles calculations. Both Al-contacted and NiGe-contacted n+/p junctions were fabricated. Phosphorus and arsenic ions were Implanted Before Germanide (IBG) formation or Implanted After Germanide (IAG) formation. The NiGe-contacted junction always exhibit higher forward current than the Al-contacted junction due to dopant segregation. First principles calculations predict that phosphorus atoms tend to segregate on both NiGe side and Ge side while arsenic atoms tend to segregate at Ge side. Since phosphorus has higher activation level and lower diffusion coefficient than arsenic, we propose a phosphorus IBG+arsenic IAG process. Shallow n+/p junction with junction depth 90nm below the NiGe/Ge interface is achieved. The lowest and average contact resistivity is 2×10−6Ωcm2 and 6.7×10−6Ωcm2, respectively. Methods which can further reduce the junction depth and contact resistivity are suggested.

Epitaxial formation of Ni germanide on Ge(0 0 1) substrate by reactive deposition

We investigated the crystalline structure of a NiGe layer grown on Ge(001) substrate through the reactive deposition method. NiGe layers grown at 350°C are a single crystalline, provided that they are thin enough—below 22nm. The epitaxial relationship with the Ge(001) substrate is then as follows: NiGe(111)//Ge(001), and NiGe[01¯1]//Ge[110]. However, the NiGe layer becomes polycrystalline when the thickness reaches 22nm or thicker. We proposed a two-step deposition method combined with solid-phase reaction to suppress the polycrystalline formation and successfully achieved an epitaxial NiGe layer over 22nm-thick with an atomically flat interface. We also clarified that the Ge atom is the dominant diffusion species during the reactive deposition and that the Ni atom dominates during the solid-phase reaction.

Electrical and Microstructural Characterization of Cu-Germanide Contacts Formed on p-Type Ge Substrate

We have investigated the electrical and microstructural properties of Cu-germanides formed on p-type Ge substrate as a function of rapid thermal annealing (RTA) temperature. As increasing RTA temperatures, Cu films reacted with Ge and formed Cu-germanides. The Cu3Ge phase appears to be the dominant phase along with Cu5Ge2 phase at annealing temperatures of 500 and 600 °C. The sheet resistance and specific contact resistivity were investigated as a function of germanide formation temperature. A minimum specific contact resistivity value of 6.19´10-6 Wcm2 is obtained after annealing at 400 °C associated with the formation of low stoichiometric Cu3Ge phase. The sheet resistance and specific contact resistivity increased after rapid thermal annealing at temperatures >500 °C, indicated the degradation of the contact properties and could be associated with the formation of copper rich Cu5Ge2 phase and the loss of structural integrity with increasing annealing temperature.

Understanding and engineering of NiGe/Ge junction formed by phosphorous ion implantation after germanidation

Modulation of the effective electron Schottky barrier height (eSBH) of NiGe/Ge contacts induced by phosphorous ion implantation after germanide formation was investigated by considering local inhomogeneity in the eSBH. Systematic studies of NiGe/Ge contact devices having various germanide thicknesses and ion implantation areas indicated the threshold dopant concentration at the NiGe/Ge interface required for eSBH modulation and negligible dopant diffusion even at NiGe/Ge interface during drive-in annealing, leading to variation in the eSBH between the bottom and sidewall portions of the NiGe regions. Consequently, this method makes it possible to design source/drain contacts with low-resistivity Ohmic and ideal rectifying characteristics for future Ge-based transistors.

Electrical and Microstructural Characterization of Cu-Germanide Contacts Formed on p-Type Ge Substrate

We have investigated the electrical and microstructural properties of Cu-germanide formed on p-type Ge substrate as a function of rapid thermal annealing (RTA) temperature. As increasing RTA temperatures, Cu films reacted with Ge and formed Cu-germanides. The Cu3Ge phase appears to be the dominant phase along with Cu5Ge2 phase at annealing temperatures of 500 and 600 °C. The sheet resistance and specific contact resistivity were investigated as a function of germanide formation temperature. A minimum specific contact resistivity value of 6.19´10-6 Ωcm2 is obtained after annealing at 400 °C associated with the formation of stoichiometric Cu3Ge. The sheet resistance and specific contact resistivity increased after rapid thermal at temperatures >500 °C indicated the degradation of the contact properties and could be associated with the formation of copper rich Cu5Ge2phase and the loss of structural integrity with increasing annealing temperature.

DLow Temperature of formation of Nickel Germanide by reaction of Nickel and Crystalline Germanium

ABSTRACTThe formation of nickel germanide has been examined over a range of low temperatures (200-400 °C) in an attempt to minimize the thermal budget for the process. Cross-sectional Transmission Electron Microscopy (TEM) was used to determine the texture of the germanide layer and the morphology and constituent composition of the Ge/NiGe interface. The onset and completion of reaction between Ni and Ge were identified by means of a heated stage in combination with in-situ x-ray diffraction (XRD) measurements. The stages of reaction were also monitored using measurements of sheet resistance of the germanides by the Van der Pauw technique. The results have shown that the minimum temperature for the initiation of reaction of Ni and Ge to form NiGe was 225 °C. However, an annealing temperature > 275 °C was necessary for the extensive (and practical) formation of NiGe. Between 200 and 300 °C, the duration of annealing required for the formation of NiGe was significantly longer than at higher temperatures. The stoichiometry of the germanide was very close to NiGe (1:1) as determined using energy dispersive spectroscopy (EDS).

Formation of nickel germanide on SiO2-capped n-Ge to lower its Schottky barrier height

In this Letter, NiGe/SiO2/n-Ge ohmic contacts were demonstrated with Ge, rather than Ni, diffusion through the ion-implanted SiO2 films to form NiGe. The equivalent Schottky barrier height reduced from 0.58 eV for NiGe/n-Ge to ohmic contact. The anomalous diffusion behavior and accumulation of Ge in the SiO2 near the NiGe/SiO2 interface can be explained by vacancy-enhanced Ge diffusion. It is proposed that the presence of vacancies and Ge atoms embedded in the SiO2 layer play a significant role in the current enhancement by generation of multiple levels in the SiO2 band gap.

Direct growth of germanium and silicon nanowires on metal films

We describe the basic thermodynamic and kinetic aspects that govern the growth of Si and Ge nanowires directly on bulk metal films. We illustrate essential differences between the vapour–solid–solid and the conventional vapour–liquid–solid nanowire growth. Ge and Si nanowires were formed on a select set of metal films including Ag, Al, Au, Cr, Cu and Ni. Metals that form silicides or germanides (Cr, Cu, and Ni) generally yield higher quality nanowires compared to nanowires grown on metal films whose equilibrium phases are defined by alloyed phases below eutectic temperatures (Al, Ag, Au). Combinatorial experiments presented here provide new basic insights into nanowire formation in the context of metal germanide and silicide formation rates. The mechanism established from our experiments successfully predicts the nanowire growth under a broad range of conditions and also predicts the nanowire growth on other metals to provide guidance to future progress in nanowire synthesis.

Microwave assisted growth of copper germanide thin films at very low temperatures

Herein the synthesis of Cu3Ge films by exposing Cu-Ge alloy films to microwave radiation is reported. It is shown that microwave radiation led to the formation of copper germanide at temperatures ca. 80 °C. The electrical properties of the Cu3Ge films are presented and compared for various annealing times. X-ray diffraction shows that the Cu3Ge films formed after microwave annealing is crystalline in the orthorhombic phase. Rutherford backscattering and X-ray photoelectron spectroscopy confirms the formation of copper oxide encapsulation layer. Despite the slight oxidation of Cu during the microwave anneal the lowest resistivity of Cu3Ge films obtained is 14 μΩ-cm.

Ge diffusion and bonding state change in metal/high-k/Ge gate stacks and its impact on electrical properties

Graphical abstractDisplay Omitted Plasma-assisted oxidation is preferable to form HfO2/GeOx/Ge structures.Al on HfO2/GeOx/Ge stack induces the reduction of GeOx and Al germanide formation.Hf germanide was formed in Pt/HfO2/GeOx/Ge stacks by annealing.Germanide formation should be suppressed for high-quality metal/high-k/Ge stack. We systematically investigated Ge diffusion and chemical bonding states in metal/high-k/Ge gate stacks by synchrotron radiation photoemission spectroscopy (SR-PES) to understand their impact on electrical properties. Although Hf germanide was found in both Ge 3s and Hf 4f spectra for HfO2/GeOx/Ge gate stacks formed by ultrathin metal Hf deposition and subsequent in situ low-pressure thermal oxidation, such germanide could be fully oxidized when using plasma-assisted oxidation. However, Al electrode deposition on HfO2/GeOx/Ge stacks was found to reduce interfacial GeOx layer, resulting in the formation of Al germanide at the Al/HfO2 interface even at room temperature. No germanide was formed in the stacks with inert Pt electrode. This indicates that the Al layer may promote upward diffusion of GeO molecules through the HfO2 layer. The thermal stability of metal/HfO2/GeOx/Ge gate stacks was also evaluated by in situ SR-PES. Hf germanide was observed to form near the HfO2/GeOx interface probably due to Ge atoms intermixing in the HfO2 layer in the Pt-gate stacks, in contrast to the enhanced formation of Al germanide in Al-gate stacks. Electrical characterization revealed that the formation of metal germanide led to severe degradation of insulating properties in metal/high-k/Ge stacks.

Formation of NiGe through germanium oxide on Ge(0 0 1) substrate

Germanium based devices are of interest due to their performance potential. The use of germanium as source and drain requires low resistance access achieved by the formation of germanide (metal-germanium compound). The nickel mono-germanide (NiGe) is claimed to be the best candidate since it presents suitable electrical and thermo-kinetic qualities. However, since the germanium oxidizes instantaneously in air, we provide in this paper a study of reactions between a nanometric Ni film and a germanium (001) substrate in the presence of a native or controlled grown germanium oxide. The goal is to study the influence of the germanium oxide onto germanidation process. We report that whatever the germanium oxide types (native or grown) formation of nickel germanides can occur unlike to silica which inhibits metal/silicon reactions. Numerous characterizations such as XRD, TEM, EFTEM, SIMS and SEM lead us to propose a model. Whatever the oxide type as thick as 8nm, nickel reacts with GeO2 during its deposition and transforms into a continuous germanate layer allowing NiGe nucleation on Ge substrate. After heat treatment the entire pure Ni film has reacted while the germanate NixOyGez were present. This means that Ni transport occurred even through germanate. Finally, this NixOyGez film shifted toward the surface as a discontinued layer.

Ohmic contact on n-type Ge using Yb-germanide

Poor ohmic contact by Fermi-level pinning to valence band (EV) edge is one of the major challenges for germanium (Ge) n-type metal–oxide–semiconductor field-effect transistor (nMOSFET). Using low work-function rare-earth ytterbium (Yb), good ohmic contact on n-type Ge with alleviated Fermi-level pinning was demonstrated. Such ohmic behavior depends strongly on the germanide formation condition, where much degraded ohmic contact at 600 °C rapid thermal annealing is due to the lower Yb/Ge composition found by energy-dispersive x-ray spectroscopy. The ohmic behavior of Yb-germanide/n-type-Ge has high potential for future high-performance Ge nMOSFET application.

Determination of the dominant diffusing species during nickel and palladium germanide formation

We have used real-time Rutherford backscattering spectrometry to determine the dominant diffusing species during the formation of nickel germanide and palladium germanide; two of the most promising candidates for use as ohmic contacts were germanium to replace silicon in devices. In the Ni/Ge system Ni5Ge3 is the first phase to form, followed by NiGe. The results show that during Ni5Ge3 formation Ni is essentially the sole diffusing species and is responsible for almost all the growth. During the 2nd-phase formation both Ni and Ge diffuse, with the Ge diffusion prominent during the very early stages, while the later stage of growth is dominated by Ni diffusion. During the formation of Pd2Ge and PdGe phases the metal (i.e. palladium) is once again the dominant diffusing species. The relative contribution of germanium diffusion to the growth is, however, more prominent in the Pd/Ge system, with significant amounts of Ge diffusion being observed during formation of both phases.

Selenium Segregation for Effective Schottky Barrier Height Reduction in NiGe/n–Ge Contacts

In this letter, we report the demonstration of an effective electron Schottky barrier height (ΦBn) reduction technology for NiGe/n-type Germanium (n-Ge) contacts using ion implantation of selenium (Se) followed by its segregation at NiGe/n-Ge interface. Se was found to segregate at NiGe/n-Ge interface after germanide formation. Nickel monogermanide was formed using a 350°C 30-s anneal. Se segregation gives ΦBn as low as ~0.13 eV.

The First-Cycle Electrochemical Lithiation of Crystalline Ge: Dopant and Orientation Dependence and Comparison with Si

We use first principles Density Functional Theory (DFT), cyclic voltammetry (CV), and Raman spectroscopy to investigate the first-cycle electrochemical lithiation of Ge in comparison with Si – both high-capacity anode materials for Li ion batteries. DFT shows a significant difference in the dilute solubility of Li in Si and Ge, despite similarities in their chemical and physical properties. We attribute this difference to electronic, as opposed to elastic, effects. CV and Raman data reveal little dopant dependence in the lithiation onset voltages in Ge, unlike in Si, due to a smaller energy difference between dilute Li insertion in p-type Ge and bulk germanide formation than the corresponding difference in Si. Finally, we show that there is no orientation dependence in lithiation onset voltages in Ge. We conclude that approaches other than microstructuring are needed to fabricate effective electrodes able to take advantage of the higher rate capability of Ge compared to that of Si.

Sn diffusion during Ni germanide growth on Ge1–xSnx

We report on the redistribution of Sn during Ni germanide formation on Ge1–xSnx/〈Ge(100)〉 and its influence on the thin film growth and properties. These results show that the reaction involves the formation of Ni5Ge3 and NiGe. Sn redistributes homogenously in both phases, in which the Sn/Ge ratio retains the ratio of the as-deposited Ge1–xSnx film. Sn continues to diffuse after full NiGe formation and segregates in two regions: (1) at the interface between the germanide and Ge1–xSnx and (2) at the surface, which has major implications for the thin film and contact properties.

Microstructural Evolution and Electrical Characteristics of Er-germanides Formed on Ge Substrate

The microstructural and electrical properties of Er-germanides formed by a solid state reaction between Er and Ge have been investigated at different germanide formation temperatures from 400 to 700°C. Er26Ge23 and Er3Ge4 phases were formed at a germanidation temperature of 400°C, followed by the formation of Er3Ge4 and Er2Ge3 at 500 to 600°C and then ErGe2.16 at 700°C. The sheet resistance gradually decreased with increasing annealing temperature up to 600°C, which could be associated with the phase transformation from Er-rich to Ge-rich Er-germanides. Er-germanides on n-type Ge showed Schottky behavior at low formation temperatures of less than 600°C. Above 600°C they exhibit Ohmic behavior. However, due to strong Fermi level pinning, Er-germanide contact to p-type Ge substrates was demonstrated to be Ohmic regardless of the annealing temperatures. The conversion of Schottky to Ohmic behavior could be attributed to a significant increase in current in the forward and reverse biases caused by the formation of square-shaped microvoids driven by Ge out-diffusion near the interface between germanides and the Ge substrate.